Rigid PUR/PIR foams are these days overwhelmingly manufactured on the basis of aromatic polyester polyols, since these have a positive influence on the flame resistance of rigid PUR/PIR foams and their thermal conductivity. The raw materials used to prepare aromatic polyester polyols are chiefly phthalic acid/anhydride, terephthalic acid and isophthalic acid. Short-chain polyether polyols and also, in some instances, aliphatic polyester polyols are sometimes used in addition to and alongside aromatic polyester polyols in order to improve the solubility of pentanes for aromatic polyester polyols or to reduce the brittleness of the rigid isocyanurate-containing PUR/PIR foams.
EP 1219653 describes rigid PUR/PIR foams of improved flame resistance and low thermal conductivity which are based on aromatic polyester polyols. In addition, the use of aliphatic, cycloaliphatic or heterocyclic polyester polyols is also proposed.
WO 97/48747 teaches that rigid PUR/PIR foams of reduced brittleness and improved surface adherence are obtainable when the polyol component comprises aliphatic as well as aromatic polyester polyols.
WO 2004/060950 further discloses rigid PUR/PIR foams for spray foam applications with improved flame resistance and improved lambda aging characteristics that are based on aromatic polyester polyols. In addition, the use of aliphatic or heterocyclic polyester polyols is also proposed.
WO 2004/060950 teaches that rigid PUR/PIR foams of high thermal resistance and improved flame resistance are obtainable when the polyol component comprises preferably high-functionality aromatic polyester polyols.
U.S. Pat. No. 6,945,722 and US 2002/0040122 describe the use of Mannich polyols in the manufacture of purely water-blown systems because only the use of such polyols provides good flame resistance and dimensional stability. One immense disadvantage of such Mannich polyols is their high viscosity and the associated processability as spray foam system. The high viscosity tends to give rise to mixing problems and hence to foams having poor mechanical-physical properties.
There is increasing demand for rigid aliphatic polyester-based PUR/PIR foams in insulating panel manufacture. According to EP 1 632 511 A1, the polyester polyols may be constructed from technical-grade glutaric acid and also ethylene glycol. By way of added-substance materials there are mentioned further formulation constituents: a polyether polyol, a flame retardant such as TCPP as well as further auxiliary and added-substance materials.
Only comparatively inexpensive feedstocks come into consideration as conceivable synthons to replace and/or supplement the technical-grade glutaric acid because of the current market situation (high price pressure in the insulant market through “commoditized” insulants such as expanded polystyrene (EPS) and mineral wool), in particular phthalic anhydride. The use of phthalic anhydride in a polyester recipe consisting otherwise of technical-grade glutaric acid and ethylene glycol leads to araliphatic esters, but these are known not to be ideal for use in the manufacture of rigid foams.
It is desirable, then, in some instances to at least initially eschew the addition of the flame retardant TCPP or to admix a flame retardant at a later stage of formulation production. This is associated with additional formulation effort, while the compatibilizing effect of the flame retardant is initially forfeited.